Cotton garments (cellulose fiber products) such as underwear have been required to have high moisture-absorption properties and high moisture-desorption properties. Such a cotton garment (cellulose fiber product) with high moisture-absorption properties and high moisture-desorption properties may be obtained by, for example, hydrophilizing cellulose fibers used as raw materials. Various methods for hydrophilizing cellulose fibers are known, and one representative example of such methods is oxidizing a hydroxy group in cellulose to a carboxy group.
A known method of oxidizing a hydroxy group in cellulose to a carboxy group is oxidizing cellulose fibers used as raw materials in a reaction solution containing a N-oxyl compound such as 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and a halogen-based oxidizing agent in the presence of a co-catalyst (see Patent Literature 1, for example).
For industrial oxidation and hydrophilization of cellulose fibers, it is desirable to reuse the reaction solution for the oxidation treatment. However, if a reaction solution is reused in oxidation of cellulose fibers with a N-oxyl compound and a halogen-based oxidizing agent, a halogen-based salt, which is a by-product of the reaction, inhibits the reaction. Thus, with a used reaction solution, it is typically difficult to introduce carboxy groups to cellulose fibers with sufficient efficiency.